1. Technical Field
The present disclosure relates to a piezoelectric vibrator element, a piezoelectric vibrator, an electronic apparatus, and a vehicle.
2. Related Art
An AT-cut quartz vibrator as a piezoelectric vibrator for exciting a thickness-shear vibration as a principal vibration is suitable for miniaturization and higher frequency, and has a frequency-temperature characteristic exhibiting an excellent cubic curve, and is therefore used in a variety of fields such as an oscillator and electronic equipment. In particular, in recent years, due to the progress in speeding up of the processing speed of transmission communication equipment and OA equipment, or increase in capacity of communication data and a processing amount, a demand of increase in frequency to the AT-cut quartz crystal vibrator as a reference frequency signal source used therefor is increasing. In order to increase the frequency of the AT-cut quartz crystal vibrator excited in the thickness-shear vibration mode, it is common practice to achieve the higher frequency by decreasing the thickness of the vibrating part.
However, if the thickness of the vibrating part is decreased due to the increase in the frequency, there is a problem that an influence of thermal strain with the excitation electrode increases to deteriorate the frequency-temperature characteristic. To cope with the above, in JP-A-11-284484, there is disclosed the fact that in the AT-cut quartz crystal vibrator for obtaining the fundamental vibration of equal to or higher than 300 MHz by forming a recessed part in a part of either one or both of the surfaces of the AT-cut quartz crystal substrate to thereby provide a super-thin vibrating part to the bottom of the recessed part and forming a whole-area electrode on one surface of the quartz crystal substrate and forming partial electrodes on the other surface, it is possible to make the vibrational frequency deviation equal to or lower than ±40 ppm in at least the temperature range of −35° C. through +80° C. by using gold as at least the film material of the whole-area electrode and at the same time arranging that the ratio tx/T between the thickness T of the super-thin vibrating part and the film thickness tx obtained by reducing the whole-area electrode into quartz crystal density becomes in a range of 5% through 13%.
However, the AT-cut quartz crystal vibrator described in JP-A-11-284484 is effective for an improvement in frequency-temperature characteristic, but has a problem that the aging characteristic is degraded.